U.S. patent application number 10/999092 was filed with the patent office on 2005-04-14 for corneal implant and method of manufacture.
Invention is credited to Nigam, Alok.
Application Number | 20050080485 10/999092 |
Document ID | / |
Family ID | 23520014 |
Filed Date | 2005-04-14 |
United States Patent
Application |
20050080485 |
Kind Code |
A1 |
Nigam, Alok |
April 14, 2005 |
Corneal implant and method of manufacture
Abstract
Prosthetic implants designed to be implanted in the cornea for
modifying the cornea curvature and altering the corneal refractive
power for correcting myopia, and myopia with astigmatism, such
implants formed of a micro-porous hydrogel material.
Inventors: |
Nigam, Alok; (Trabuco
Canyon, CA) |
Correspondence
Address: |
FULBRIGHT & JAWORSKI, LLP
1301 MCKINNEY
SUITE 5100
HOUSTON
TX
77010-3095
US
|
Family ID: |
23520014 |
Appl. No.: |
10/999092 |
Filed: |
November 29, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10999092 |
Nov 29, 2004 |
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10047726 |
Jan 15, 2002 |
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10047726 |
Jan 15, 2002 |
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09385103 |
Aug 27, 1999 |
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6361560 |
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09385103 |
Aug 27, 1999 |
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09219594 |
Dec 23, 1998 |
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6102946 |
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Current U.S.
Class: |
623/5.16 ;
623/5.11 |
Current CPC
Class: |
A61F 2/147 20130101 |
Class at
Publication: |
623/005.16 ;
623/005.11 |
International
Class: |
A61F 002/14 |
Claims
I claim:
1. A corneal implant, comprising: a body formed of an optically
clear, biocompatible material having an index of refraction ranging
from 1.36 to 1.39, the body having anterior and posterior surfaces,
the biocompatible material having micropores sized to act as a
barrier against tissue in growth, the micropores adapted to permit
nutrient and fluid transfer to prevent tissue necrosis.
2. The corneal implant of claim 1, wherein the micropores range in
diameter from 50 Angstroms to 10 microns.
3. The corneal implant of claim 1, wherein the biocompatible
material is a microporous hydrogel.
4. The corneal implant of claim 3, wherein the microporous hydrogel
has a water content greater than 40% up to approximately 90%.
6. The corneal implant of claim 3, wherein the microporous hydrogel
is made from at least one hydrophilic monomer which is polymerized
and cross-linked with at least one-multi- or di-olefinic
cross-linking agent.
7. The corneal implant of claim 1, wherein the body has an outer
edge with a thickness less than about 15 micrometers.
8. The corneal implant of claim 1, wherein the body has an outer
edge thickness being no greater than the dimensions of two
keratocytes juxtaposed side-by-side.
9. The corneal implant of claim 1, wherein the body being solid and
having two surfaces that are bi-meniscus in shape and joining each
other at the periphery of the lens.
10. The corneal implant of claim 1, wherein the body is generally
circular in shape.
11. The corneal implant of claim 1, wherein the anterior and
posterior surfaces have different radii of curvature.
12. The corneal implant of claim 1, wherein the anterior surface
has a greater radius than the posterior surface.
13. The corneal implant of claim 1, wherein the body is of a size
greater than the size of the pupil in normal or bright light.
14. The corneal implant of claim 1, wherein the body is shaped to
correct for hyperopia.
15. The corneal implant of claim 1, wherein the body is shaped to
correct for myopia.
16. The corneal implant of claim 1, wherein the body is shaped to
correct for astigmatism.
17. The corneal implant of claim 1, wherein the body is shaped to
correct for presbyopia.
18. The corneal implant of claim 1, wherein the body is about 4.5
mm in diameter.
19. The corneal implant of claim 1, wherein the center of the body
is no greater than 50 micrometers thick.
20. The corneal implant of claim 1, wherein the body has a
transition zone between the anterior and posterior surfaces.
21. The cornmeal implant of claim 1, wherein the body is configured
for multi-focal outer corneal surface correction.
22. The corneal implant of claim 1, wherein the body has a central
power add portion.
23. The corneal implant of claim 22, wherein the central power add
portion has a diameter in the range of 1.5-3 mm.
24. The corneal implant of claim 22, wherein a transition zone is
formed around the central power add.
25. The corneal implant of claim 24, wherein the transition zone
provides a change in power from the central power add to a
peripheral base power of the body.
26. The corneal implant of claim 1, wherein the body has varied
thickness thereby providing different diopter powers to correct for
an astigmatism.
27. A corneal implant; comprising: a body formed of an optically
clear, biocompatible material having an index of refraction ranging
from 1.36 to 1.39, the body having anterior and posterior surfaces,
the body having a center that is no greater than 50 micrometers
thick, the biocompatible material having micropores sized to act as
a barrier against tissue in growth, the biocompatible material
having a water content greater than 40% up to approximately 90%,
and the micropores adapted to permit nutrient and fluid transfer to
prevent tissue necrosis.
28. The corneal implant of claim 27, wherein the body is generally
circular in shape.
29. The corneal implant of claim 27, wherein the anterior and
posterior surfaces have different radii of curvature.
30. The corneal implant of claim 27, wherein the anterior surface
has a greater radius than the posterior surface.
31. The corneal implant of claim 27, wherein the body is of a size
greater than the size of the pupil in normal or bright light.
32. The corneal implant of claim 27, wherein the body is shaped to
correct for hyperopia.
33. The corneal implant of claim 27, wherein the body is shaped to
correct for myopia.
34. The corneal implant of claim 27, wherein the body is shaped to
correct for astigmatism.
35. The corneal implant of claim 27, wherein the body is shaped to
correct for presbyopia.
36. The corneal implant of claim 27, wherein the body is about 4.5
mm in diameter.
37. The corneal implant of claim.27, wherein the body has a
transition zone between the anterior and posterior surfaces.
38. The corneal implant of claim 27, wherein the body is configured
for multi-focal outer corneal surface correction.
39. The corneal implant of claim 27, wherein the body has a central
power add portion.
40. The corneal implant of claim 39, wherein the central power add
portion has a diameter in the range of 1.5-3 mm.
41. The corneal implant of claim 39, wherein a transition zone is
formed around the central power add.
42. The corneal implant of claim 41, wherein the transition zone
provides a change in power from the central power add to a
peripheral base power of the body.
43. The corneal implant of claim 27, wherein the body has varied
thickness thereby providing different diopter powers to correct for
an astigmatism.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of application Ser. No.
10/047,726, filed Jan. 15, 2002, which is a continuation of U.S.
patent application Ser. No. 09/385,103, filed Aug. 27, 1999, now
U.S. Pat. No. 6,361,560, which is a continuation-in-part of U.S.
patent application Ser. No. 09/219,594, filed Dec. 23, 1998, now
U.S. Pat. No. 6,102,946.
FIELD OF THE INVENTION
[0002] The field of this invention relates to prosthetic implants
designed to be implanted in the cornea for modifying the cornea
curvature and altering the corneal refractive power for correcting
myopia, hyperopia, astigmatism, and presbyopia, and, in addition,
to such implants formed of a micro-porous hydrogel material.
BACKGROUND OF THE INVENTION
[0003] It is well known that anomalies in the shape of the eye can
be the cause of visual disorders. Normal vision occurs when light
that passes through and is refracted by the cornea, the lens, and
other portions of the eye, and converges at or near the retina.
Myopia or near-sightedness occurs when the light converges at a
point before it reaches the retina and, conversely, hyperopia or
far-sightedness occurs when the light converges a point beyond the
retina. Other abnormal conditions include astigmatism where the
outer surface of the cornea is irregular in shape and effects the
ability of light to be refracted by the cornea. In addition, in
patients who are older, a condition called presbyopia occurs in
which there is a diminished power of accommodation of the natural
lens resulting from the loss of elasticity of the lens, typically
becoming significant after the age of 45.
[0004] Corrections for these conditions through the use of implants
within the body of the cornea have been suggested. Various designs
for such implants include solid and split-ring shaped, circular
flexible body members and other types of ring-shaped devices that
are adjustable. These implants are inserted within the body of the
cornea for changing the shape of the cornea, thereby altering the
its refractive power.
[0005] These types of prostheses typically are implanted by first
making a tunnel and/or pocket within the cornea which leaves the
Bowman's membrane intact and hence does not relieve the inherent
natural tension of the membrane.
[0006] In the case of hyperopia, the corneal curvature must be
steepened, and in the correction of myopia, it must be flattened.
The correction of astigmatism can be done by flattening or
steepening various portions of the cornea to correct the irregular
shape of the outer surface. Bi-focal implants can be used to
correct for presbyopia.
[0007] It has been recognized that desirable materials for these
types of prostheses include various types of hydrogels. Hydrogels
are considered desirable because they are hydrophilic in nature and
have the ability to transmitting fluid through the material. It has
been accepted that this transmission of fluid also operates to
transmit nutrients from the distal surface of the implant to the
proximal surface for providing proper nourishment to the tissue in
the outer portion of the cornea.
[0008] However, while hydrogel lenses do operate to provide fluid
transfer through the materials, it has been found that nutrient
transfer is problematic because of the nature of fluid transfer
from cell-to-cell within the material. Nutrients do not pass
through the hydrogel material with the same level of efficacy as
water. Without the proper transfer of nutrients, tissue in the
outer portion of the cornea will die causing further deterioration
in a patient's eyesight.
[0009] Thus, there is believed to be a demonstrated need for a
material for corneal implants that will allow for the efficacious
transmission of nutrients from the inner surface of a corneal
implant to the outer surface, so that tissue in the outer portion
of the cornea is properly nourished. There is also a need for a
more effective corneal implant for solving the problems discussed
above.
DESCRIPTION OF THE PRIOR ART
SUMMARY OF THE INVENTION
[0010] The present invention is directed to a corneal implant
formed of a biocompatible, permeable, micro-porous hydrogel with a
refractive index substantially similar to the refractive index of
the cornea. The device, when placed under a lamellar dissection
made in the cornea (such as a corneal flap), to relieve tension of
Bowman's membrane, alters the outer surface of the cornea to
correct the refractive error of the eye. By relieving the pressure
and subsequent implantation of the device, the pressure points
which typically are generated in present corneal surgeries are
eliminated, and hence reduced risk to patients of extrusion of
implants.
[0011] The implant is preferably generally circular in shape and is
of a size greater than the size of the pupil in normal or bright
light, and can specifically be used to correct hyperopia, myopia,
astigmatism, and/or presbyopia. Due to the complete non-elastic
nature of the corneal tissue, it is necessary to place the implant
in the cornea with Bowman's membrane compromised, such as through a
corneal lamellar dissection, to prevent extrusion of the implant
from the cornea over the lifetime of the implant. Extrusion is
undesirable because it tends to cause clinical complications and
product failure.
[0012] Preferably, for the correction of hyperopia, the implant is
formed into a meniscus-shaped disc with its anterior surface radius
smaller (steeper) than the posterior surface radius, and with
negligible edge thickness. This design results in a device-that has
a thickness or dimension between the anterior and posterior
surfaces along the central axis greater than at its periphery. When
such an implant is placed under the corneal flap, the optical zone
of the cornea is steepened and a positive optical power addition is
achieved.
[0013] For the correction of myopia, the implant is shaped into a
meniscus lens with an anterior surface curvature that is flatter
than the posterior surface. When the implant is placed
concentrically on the stromal bed the curvature of the anterior
surface of the cornea in the optic zone is flattened to the extent
appropriate to achieve the desired refractive correction.
[0014] For astigmatic eyes, implants are fabricated with a
cylindrical addition along one of the axes. This device can be oval
or elliptical in shape, with a longer axis either in the direction
of cylindrical power addition or perpendicular to it. The implant
preferably has a pair of markers such as, for example, protrusions,
indentations or other types of visual indicators, in the direction
of the cylindrical axis to easily mark and identify this direction.
This indexing assists the surgeon in the proper placement of the
implant under the flap with the correct orientation during surgery
to correct astigmatism in any axis.
[0015] For simple or compound presbyopia, the implant is made by
modifying the radius of curvature in the central 11.5-3 mm, thereby
forming a multi-focal outer corneal surface where the central
portion of the cornea achieves an added plus power for close-up
work. The base of an implant designed for compound presbyopia can
have a design to alter the cornea to achieve any desired correction
for the myopic, hyperopic, or astigmatic eye.
[0016] The material from which any one or more of these implants
are made is preferably a clear, permeably, microporous hydrogel
with a water content greater than 40% up to approximately 90%. The
refractive index should be substantially identical to the
refractive index of corneal tissue. The permeability of the
material is effected through a network of irregular passageways
such as to permit adequate nutrient and fluid transfer to prevent
tissue necrosis, but which are small enough to act as a barrier
against the tissue ingrowth from one side of the implant to
another. This helps the transmembrane tissue viability while
continuing to make the implant removable and exchangeable.
[0017] The refractive index of the implant material should be in
the range of 1.36-1.39, which is substantially similar to that of
the cornea (1.376). This substantially similar refractive index
prevents optical aberrations due to edge effects at the
cornea-implant interface.
[0018] The microporous hydrogel material can be formed from at
least one (and preferably more) hydrophilic monomer, which is
polymerized and cross-linked with at least one multi- or
di-olefinic cross-linking agent.
[0019] The implants described above can be placed in the cornea by
making a substantially circular lamellar flap using any
commercially available microkeratome. When the flap is formed, a
hinge is preferably left to facilitate proper alignment of the
dissected corneal tissue after the implant is placed on the exposed
cornea.
[0020] The implants described above which can be used for
correcting hyperopia or hyperopia with astigmatism are preferably
made into a disc shape that is nominally about 4.5 mm in diameter
and bi-meniscus in shape. The center of the lens is preferably no
greater than 50 micrometers thick. The edge thickness should be
less than two keratocytes (i.e., about 15 micrometers).
[0021] An improvement over the lenses described above for
correcting myopia with astigmatism includes forming a lens in the
shape of a ring with one or more portions in the center being solid
and defining voids in the center section for shaping the astigmatic
component by providing solid portions under the flatter meridian of
the astigmatic myopic eye. An example of such a shape includes a
ring with a rib extending across the center that is either squared
off or rounded where it contacts the ring. Another example is a
ring with one or more quadrants filled in, with the other ones
forming voids. Other shapes can used to provide a solid portion
under the flatter meridan.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] A better understanding of the invention can be obtained from
the detailed description of exemplary embodiments set forth below,
when considered in conjunction with the appended drawings, in
which:
[0023] FIG. 1 is a schematic illustration of a horizontal section
of a human eye;
[0024] FIG. 2 is a schematic illustration of an eye system showing
adjustment of the cornea to steepen the corneal slope to correct
for hyperopia;
[0025] FIG. 3 is a schematic illustration of an eye system showing
adjustment of the cornea to flatten the corneal slope to correct
for myopia;
[0026] FIGS. 4a and 4b are sectional and plan views of a solid
corneal implant for correcting hyperopia;
[0027] FIGS. 5a and 5b are sectional and plan views of a solid
corneal implant for correcting myopia;
[0028] FIGS. 6a and 6b are sectional and plan views of ring-shaped
corneal implant for correcting myopia;
[0029] FIGS. 7a and 7b are schematic representations of a lamellar
dissectomy, with FIG. 7b showing in particular the portion of the
dissected cornea being connected through a hinge to the intact
cornea;
[0030] FIG. 8 is a schematic representations of a cornea in which
an implant has been implanted for a hyperopic correction;
[0031] FIGS. 9 and 10 are schematic representations of a cornea in
which solid and ring-shaped implants, respectively, have been
implanted lamellar for a myopic correction;
[0032] FIGS. 11a, 1b, and 11c are plan and sectional views of an
implant useful for correcting astigmatism where two axes have
different diopter powers;
[0033] FIGS. 12a, 12b, and 12c are plan and sectional views of an
second implant for correcting astigmatism where the implant is
elliptical in shape;
[0034] FIG. 13 is a plan view of an implant with a pair of tabs
used to identify an axis for astigmatic correction;
[0035] FIG. 14 is a plan view of a second implant for astigmatic
correction where indentations are used instead of tabs;
[0036] FIGS. 15 and 16 are schematic representations showing
implants with tabs orientated along the astigmatic-axis for
correcting astigmatism;
[0037] FIG. 17 is a sectional view of a corneal implant shaped to
correct for compound presbyopia with an additional power in the
center of an implant for correcting hyperopia;
[0038] FIG. 18 is a sectional view of another corneal implant
shaped to correct for compound presbyopia with additional power in
the center of an implant for correcting myopia;
[0039] FIG. 19 is a sectional view of a corneal implant with
additional power in the center for correcting simple
presbyopia;
[0040] FIG. 20a is a schematic representation of a corneal implant
for an astigmatic correction with a central power add for
correcting presbyopia, showing in particular a pair of tabs for
proper alignment of the lens;
[0041] FIG. 20b is a schematic representation of a another corneal
implant with a center power add for non-astigmatic correction,
which shows in particular a steep transition between the central
add and the remainder of the implant;
[0042] FIGS. 21a and 21b are schematic representations showing the
use of a lamellar dissection for implanting a lens of the type
shown in FIG. 20b; and
[0043] FIGS. 22 and 23 are schematic representations of several
lenses useful for correcting myopia with astigmatism formed in the
shape of a ring with a rib extending across the center of the lens;
and
[0044] FIG. 24 is another schematic representation of another lens
for correcting myopia with astigmatism where the ring-shaped lens
has one quadrant that is solid, while the rest of the center
portion forms a void.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0045] Referring first to FIG. 1 of the drawings, a schematic
representation of the globe of the eye 10 is shown, which resembles
a sphere with an anterior bulged spherical portion 12 that
represents the cornea. The eye 10 is made up of three concentric
coverings that enclose the various transparent media through which
light must pass before reaching the light sensitive retina 14.
[0046] The outer-most covering is a fibrous protective portion that
includes a posterior layer which is white and opaque, called the
sclera 16, which is sometimes referred to as the white of the eye
where it is visible from the front. The anterior 1/6th of this
outer layer is the transparent cornea 12.
[0047] A middle covering is mainly vascular and nutritive in
function and is made up of the choroid 18, the ciliary 20 and the
iris 22. The choroid generally functions to maintain the retina.
The ciliary muscle 21 is involved in suspending the lens 24 and
accommodating the lens. The iris 22 is the most anterior portion of
the middle covering of the eye and is arranged in a frontal plane.
The iris is a thin circular disc corresponding to the diaphragm of
a camera, and is perforated near its center by a circular aperture
called the pupil 26. The size of the pupil varies to regulate the
amount of light that reaches the retina 14. It contracts also to
accommodate, which serves to sharpen the focus by diminishing
spherical aberrations. The iris 22 divides the space between the
cornea 12 and the lens. 24 into an anterior chamber 28 and
posterior chamber 30.
[0048] The inner-most covering is the retina 14, consisting of
nerve elements which form the true receptive portion for visual
impressions that are transmitted to the brain. The vitreous 32 is a
transparent gelatinous mass which fills the posterior 4/5ths the
globe 10. The vitreous supports the ciliary body 20 and the retina
14.
[0049] Referring to FIG. 2 of the drawings, the globe of an eye 10
is shown as having a cornea 12 with a normal curvature represented
by a solid line 34. For people with normal vision, when parallel
rays of light 36 pass through the corneal surface 34, they are
refracted by the corneal surfaces to converge eventually near the
retina 14 (FIG. 1). The diagram of FIG. 2 discounts, for the
purposes of this discussion, the refractive effect of the lens or
other portions of the eye. However, as depicted in FIG. 2, when the
eye is hyperopic the rays of light 36 are refracted to converge at
a point 38 behind the retina.
[0050] If the outer surface of the cornea 12 is caused to steepen,
as shown by dotted lines 40, such as through the implantation of a
corneal implant of an appropriate shape as discussed below, the
rays of light 36 are refracted from the steeper surface at a
greater angle as shown by dotted lines 42, causing the light to
focus at a shorter distance, such as directly on the retina 14.
[0051] FIG. 3 shows a similar eye system to that of FIG. 2. except
that the normal corneal curvature causes the light rays 36 to focus
at a point 44 in the vitreous which is short of the retinal
surface. This is typical of a myopic eye. If the cornea is
flattened as shown by dotted lines 46 through the use of a
properly-shaped corneal implant, light rays 36 will be refracted at
a smaller angle and converge at a more distant point such as
directly on the retina 14 as shown by dotted lines 48.
[0052] A hyperopic eye of the type shown in FIG. 2 can be corrected
by implanting an implant 50 having a shape as shown in FIGS. 4a,
4b. The implant 50 is in the shape of a meniscus lens with an outer
surface 52 that has a radius of curvature that is smaller than the
radius of curvature of the inner surface 54. When a lens of this
type is implanted using the method discussed below, it will cause
the outer surface of the cornea to become steeper in shape as shown
by reference numeral 40 in FIG. 2, correcting the patient's vision
so that light entering the eye will converge on the retina as shown
by the dotted lines 42 in FIG. 2.
[0053] The lens 50 shown in FIGS. 4a and 4b is formed with a
bi-meniscus shape, with the anterior and posterior surfaces having
different radii of curvature.
[0054] The anterior surface has a greater radius than the posterior
surface. The lens 50 preferably has a nominal diameter of about 4.5
mm. The center of the lens is preferably no greater than 50
micrometers thick to enhance the diffusion characteristics of the
material from which the lens is formed, which allows for more
effective transmission of nutrients through the lens material and
promotes better health of the anterior corneal tissue. The outer
edge of the lens 50 has a thickness that is less than the
dimensions of two keratocytes (i.e., about 15 micrometers)
juxtaposed side-by-side, which are the fixed flattened connective
tissue cells between the lamellae of the cornea. An edge thickness
as specified prevents stacking and recruitment of keratocytes in
the lens material so that keratocyte stacking and recruitment does
not take place. This in turn eliminates unorganized collagen that
forms undesirable scar tissue and infiltrates the lens, which tends
to compromise the efficacy of the lens.
[0055] On the other hand, in order to cure myopia, an implant 56
having the shape shown in FIGS. 5a, 5b, can be used where an outer
surface 58 is flatter or formed with a larger radius than that of
the inner surface 60 which is formed with a radius of curvature
substantially identical to that of the corneal stroma bed generated
by the lamellar dissection described below. The implant 56 has a
transition zone 62 formed between the outer and inner surfaces 58,
60, which is outside of the optical zone. In this way, the
curvature of the outer surface of the cornea, as shown in FIG. 3,
is flattened to an extent appropriate to achieve the proper
refractive correction desired so that light entering the eye will
converge on the retina as shown in FIG. 3.
[0056] Alternatively, instead of using a solid implant as shown in
FIGS. 5a, 5b, for correcting myopia, a ring 64 of the type shown
in. FIGS. 6a, 6b could be used. This ring has substantially the
same effect as the implant shown in FIGS. 5a, 5b, by flattening the
outer surface of the cornea shown in FIG. 3. The ring 64 has a
center opening 66 that is preferably larger than the optical zone
so as not to cause spherical aberrations in light entering the
eye.
[0057] Implants of the type shown in FIGS. 4, 5 and 6 can be
implanted in the cornea using a lamellar dissectomy shown
schematically in FIGS. 7a, 7b. In this procedure, a keratome (not
shown) is used in a known way to cut a portion of the outer surface
of the cornea 12 along dotted lines 68 as shown in FIG. 7a. This
type of cut is used to form a corneal flap 70 shown in FIG. 7b,
which remains attached to the cornea 12 through what is called a
hinge 72. The hinge 72 is useful for allowing the flap 70 to be
replaced with the same orientation as before the cut.
[0058] As is also known in the art, the flap is cut deeply enough
to dissect the Bowman's membrane portion of the cornea, such as in
keratome surgery or for subsequent removal of the tissue by laser
or surgical removal. A corneal flap of 100 to 200 microns,
typically 160 to 180 microns, will be made to eliminate the
Bowman's membrane tension. This reduces the possibility of
extrusion of the implants due to pressure generated within the
cornea caused by the addition of the implant. Implants of the type
shown in FIGS. 4, 5 and 6 are shown implanted in corneas in FIGS.
8, 9 and 10, respectively, after the flap has been replaced in its
normal position. These figures show the corrected shape for the
outer surface of the cornea as a result of implants of the shapes
described.
[0059] Implants can also be formed with a cylindrical addition in
one axis of the lens in order to correct for astigmatism, as shown
in the implants in FIGS. 11-16. Such implants can be oval or
elliptical in shape, which the longer axis either in the direction
of cylindrical power addition or perpendicular to it. For example,
the implant can be circular as shown in FIG. 1 la where the,
implant 72 has axes identified as x, y. In the case of a circular
implant 72, the axes of the implant have different diopter powers
as shown in FIGS. 11b and 11bc, which are cross-sectional views of
the implant 72 along the x and y axes, respectively. The different
thicknesses of the lenses in FIGS. 11b and 11c illustrate the
different diopter powers along these axes.
[0060] Alternatively, as shown in FIG. 5a, an astigmatic implant 74
can be oval or elliptical in shape. The implant 74 also has axes x,
y. As shown in the cross-sectional views of the implant 74 in FIGS.
12b, 12c, along those two axes, respectively, the implant has
different diopter powers as shown by the different thicknesses in
the figures.
[0061] Because implants of the type identified by reference numeral
72, 74 are relatively small and transparent, it is difficult for
the surgeon to maintain proper orientation along the x and y axes.
In order to assist the surgeon, tabs 76a, 76b or indentations 78a,
78b are used to identify one or the other of the axis of the
implant to maintain proper alignment during implantation. This is
shown in FIGS. 15, 16 where, for example, indentations 76a, 76b,
are aligned with axis x which has been determined as the proper
axis for alignment in order to effect the astigmatic correction.
Alternatively, other types of markers could be used such as visual
indicators such as markings on or in the implants outside of the
optical zone.
[0062] Referring to FIGS. 17-21, implants with presbyopic
corrections are shown. In FIG. 17, an compound implant 80 is shown,
which is appropriate for hyperopic correction, which has an
additional power section 82 in the center. As shown, the implant 82
has anterior and posterior curvatures similar to those in FIGS. 4a,
4b, in order to correct for hyperopia. In FIG. 18, a central power
add 84 is formed on another compound implant 86, which has a base
shape similar to the one shown in FIGS. 5a, 5b, and is appropriate
for a myopic correction. In FIG. 19, a central power portion 88 is
added to an simple planar implant 90 which has outer and inner
surfaces of equal radii, which does not add any correction other
than the central power.
[0063] The central power add portions 82, 84, and 88 are preferably
within the range of 1.5-3 mm in diameter, most preferably 2mm, and
which provide a multi-focal outer corneal surface where the central
portion of the cornea achieves an added plus power for close-up
work. In addition to the based device having no correction, or
corrections for hyperopia or myopia, the base device can have a
simple spherical correction for astigmatism as shown in FIG. 20a ,
where a central power add 92 is added to an implant 94 similar to
the one shown in FIG. 11a, which also includes tabs 76a, 76b.
[0064] As shown in FIG. 20b in order to enhance the acuity of a
presbyopic implant, a transition zone 96 can be formed around the
central power add 98 for implant 100. This transition zone 96 is a
sharp zone change in power from central added power to peripheral
base power and is anchored over a radial distance 0.5 to 0.2 mm
start to from the end of the central zone.
[0065] Implantation of the device shown in FIG. 20b, is illustrated
in FIGS. 21a, 21b, where a flap 102 formed through a lamellar
dissectomy is shown pulled back in FIG. 21a so that the implant 100
can be positioned, and then replaced as shown in FIG. 21b for the
presbyopic correction. As shown, the formation of a sharp
transition 96 on the implant 100 provides a well defined central
power after implantation is complete.
[0066] FIGS. 22 and 23 illustrate lenses 166, 168, respectively,
which are useful for correcting myopia with astigmatism. As shown,
these lenses are ring-shaped, similar to the one in FIGS. 6a, 6b.
However, the lenses 166,168 include rib sections 166a, 168a,
respectively, which extend across the center of each lens and
define voids between the ribs and the outer periphery of the
lenses. These solid rib sections shape the astigmatic component by
providing solid portions under the flatter meridian of the
astigmatic myopic eye, when these flatter portions are located
above the ribs. The ribs 166a, 168a can be formed in any suitable
shape such as, by way of example, the rib 166a being squared off as
shown in FIG. 22 or the rib 168a being rounded s shown in FIG. 23,
where they contact their respective rings.
[0067] Another example of a design for correcting myopia with
astigmatism is a lens 170 as shown in FIG. 24, which is also
ring-shaped but has one its quadrants 170a filled in. This lens can
be used where the flatter portion of an astigmatic eye is located
in a position where the quadrant can be located beneath the flatter
portion. The solid portion of the lens will tend to raise the
flattened portion so that a smooth rounded outer surface is formed.
As can readily be appreciated, lenses can be formed with solid
portions located in any number of places where they can positioned
under the flattened portion of an astigmatic eye to achieve the
same end.
[0068] The implants described above are preferably formed of a
microporous hydrogel material in order to provide for the
efficacious transmission of nutrients from the inner to the outer
surface of the implants. The hydrogels also preferably have
micropores in the form of irregular passageways, which are small
enough to screen against tissue ingrowth, but large enough to allow
for nutrients to be transmitted. These microporous hydrogels are
different from non-microporous hydrogels because they allow fluid
containing nutrients to be transmitted between the cells that make
up the material, not from cell-to-cell such as in normal hydrogel
materials. Hydrogels of this type can be formed from at least one,
and preferably more, hydrophillic monomer which is polymerized and
cross-linked with at least one multi-or di-olefinic cross-linking
agent.
[0069] An important aspect of the materials of the present
invention is that the microporous hydrogel have micropores in the
hydrogel. Such micropores should in general have a diameter ranging
from 50 Angstroms to 10 microns, more particularly ranging from 50
Angstroms to 1 micron. A microporous hydrogel in accordance with
the present invention can be made from any of the following
methods.
[0070] Hydrogels can be synthesized as a zero gel by ultraviolet or
thermal curing of hydrophillic monomers and low levels of
cross-linking agents such as diacrylates and other UV or thermal
initiators. These lightly cross-linked hydrogels are then machined
into appropriate physical dimensions and hydrated in water at
elevated temperatures. Upon complete hydration, hydrogel prosthesis
are flash-frozen to temperatures below negative 40.degree. c., and
then gradually warmed to a temperature of negative 20.degree. c. to
negative 10.degree. c. and maintained at the same temperature for
some time, typically 12 to 48 hours, in order to grow ice crystals
to larger dimensions to generate the porous structure via expanding
ice crystals. The frozen and annealed hydrogel is then quickly
thawed to yield the microporous hydrogel device. Alternatively, the
hydrated hydrogel device can be lyophilized and rehydrated to yield
a microporous hydrogel.
[0071] Still further, the microporous hydrogel can also be made by
starting with-a known formulation of monomers which can yield a
desired cross-linked hydrogel, dissolving in said monomer mixture a
low molecular weight polymer as a filler which is soluble in said
mixture and then polymerizing the mixture. Resulted polymer is
converted into the required device shape and then extracted with an
appropriate solvent to extract out the filled polymer and the
result in a matrix hydrated to yield a microporous device.
[0072] Still further and alternatively, microporous hydrogels can
also be made by any of the above methods with the modification of
adding an adequate amount of solvent or water to give a pre-swollen
finished hydrogel, which can then be purified by extraction. Such
formulation can be directly cast molded in a desired configuration
and do not require subsequent machining processes for
converting.
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